Grout Coverage Chart: Square Feet per 25 lb Bag by Tile Size and Joint

The question that does not have an answer

"How many square feet does a 25 lb bag of grout cover?" is the most-asked question about grout, and it cannot be answered as asked. Not because the manufacturers are being cagey — because the bag does not decide.

You do not have to take our word for it. Open CUSTOM's own coverage chart for Polyblend sanded grout and read the two corners of it. One 25 lb bag covers 24 square feet of 1 inch mosaic with a 1/2 inch joint. The same bag covers 688 square feet of 24 x 24 tile with a 1/8 inch joint. Same product, same weight, same page — and a twenty-nine-fold spread between the first row and the last.

MAPEI's chart for Keracolor S is worse: from 7 square feet of 1 inch mosaic with a 5/8 inch joint to 768 of 24 x 24 with a 1/8 inch joint. A spread of a hundred and ten.

So when a page tells you a 25 lb bag covers about 70 square feet, it is not lying. It is answering for one particular tile and one particular joint, and not telling you which. Grout fills the space between the tiles. Change the tile and you change the answer, and nothing about the bag has moved.

There is no waste allowance in the number on the bag

This is the part that costs money, and it is the reason this page exists.

Almost everyone assumes a manufacturer's coverage chart is conservative — that the number has a cushion in it, because a company would rather you bought one bag too many than one too few. That assumption is comfortable and, for the tile most people are laying, it is wrong.

We took CUSTOM's chart apart. For every one of its eighty cells we worked out what density of mixed grout would have to be true for that figure to come out. The answer is the same number over and over: about 112.5 lb per cubic foot, which is simply what mixed sanded grout weighs. Feed that one number into the joint geometry and it reproduces the published chart to within 4% on every row from 6 inch tile upward.

In other words, the chart is the volume of the joints. Nothing else is in there. Not what stays in the bucket, not what stays on the float, not what you wipe off with the sponge, not the bag you tore badly, and not the extra you mixed because the first batch went off.

MAPEI's chart behaves the same way on large-format tile: back-solved, it sits at 101 to 105 lb per cubic foot. Same idea, slightly lighter grout, no cushion either.

Two things follow, and they point the same way. First, plan for 15 to 20% over the chart figure, and take that out of your own pocket rather than expecting the manufacturer to have done it for you. Second, the chart is still the right thing to shop from — it is honest arithmetic, correctly done. It just answers a narrower question than most people think it does.

Where the two brands part company

The second table is the one worth staring at, because it says something you will not find anywhere else: two of the most widely sold grouts in the United States do not agree with each other, and the disagreement is not noise.

On large-format tile they are close. For 12 x 12 with a 1/8 inch joint, CUSTOM says 348 square feet and MAPEI says 383 — about 10% apart, and our own geometry lands at 354, right between them. Fine.

Then walk up the rows toward the mosaic and the gap opens like a fan. At 1 inch mosaic with a 1/2 inch joint, MAPEI's figure is 58% below CUSTOM's. Across the whole shared range the two charts span a factor of 2.7.

The reason is not that one of them is careless. It is that mosaic is where raw joint volume stops describing the job. Sheet-mounted mosaic has mesh sitting in the joint, an enormous amount of edge per square foot, and a much larger share of every batch that never reaches a joint at all. MAPEI builds a heavy cushion in there: run their 1 inch mosaic row backward and it implies mixed grout weighing 276 lb per cubic foot, which is nearly twice what concrete weighs and therefore not a density, it is a safety margin wearing one. CUSTOM stays close to the raw volume and lets you find out.

Practically: on mosaic, buy off the lower of the two figures and then add waste on top of that. The first table on this page already takes the lower figure for you.

Here is what that is worth in bags. A hundred square feet of 1 inch mosaic with a 1/4 inch joint comes out at four bags off CUSTOM's chart, five off MAPEI's, and six once you take the prudent figure and add 20% for what the bucket keeps. Four versus six is not a rounding argument. It is a second trip to the store partway through a floor, with a bucket of grout going off behind you — MAPEI puts the pot life of a mixed batch at about an hour, and that hour is not spent driving.

Thickness is the multiplier nobody quotes

Every row in the tables above carries the tile thickness, and that is deliberate: a chart row that says "12 x 12" without saying how thick is not answering the question.

Grout fills a joint that is as deep as the tile is thick, so thickness is a straight multiplier on the volume. MAPEI's own chart proves it without any help from us, and the fourth table above is that proof: they list 6 x 6 tile twice, once at 1/4 inch thick and once at 1/2 inch, and every one of the five joint columns comes out at half, to within the rounding to whole square feet. Same tile face, same joint, double the thickness, half the coverage.

This matters more than it used to. Porcelain plank has been getting thicker, outdoor pavers run 3/4 inch and up, and a lot of the "coverage" advice floating around the internet was written when 1/4 inch tile was normal. If you are shopping off a figure that came from somewhere without a thickness attached, you are probably reading a number for a thinner tile than the one in your hand.

How to shop off these tables

1. Measure the tile you actually bought, on the edge, with a tape — thickness included. What the box says is a nominal figure and the two are often different.
2. Find your row and your joint column in the first table. If your exact size is not there, take the nearest row that is smaller than your tile; that errs toward more grout.
3. Divide your square footage by that number, then add 15 to 20%.
4. Round up to whole bags, and if you land close to the line, go up. An unopened bag goes back to the store. Running out does not have a tidy version.

For a floor of 800 square feet in 12 x 24 tile with a 1/8 inch joint, the chart figure is 461 square feet per bag. Straight division says two bags. With 20% for waste it says three. Buy three.

What the chart cannot know

The tables above assume the joint is filled to the full depth of the tile and to a flat face. Real jobs depart from that in both directions, and the departures do not cancel.

Joints that are not filled to full depth — very common on wall tile, where the grout is struck slightly concave — use less than the table says. Tile with a pronounced bevel or a pressed edge uses more, because the top of the joint is wider than the bottom is. Uneven tile, where you are filling lippage with grout, uses much more. A floor with a lot of small cuts around fixtures has more joint per square foot than the geometry of a clean field.

None of that is a reason to distrust the chart. It is a reason to treat the chart as the floor of the estimate rather than the middle of it, which is the same conclusion the waste allowance already pushes you to.

And when the bag in your hand carries its own chart, that chart wins. There are dozens of grout lines in the market, coverage moves between product families from the same manufacturer, and epoxy is a different material with different tables entirely. The value of the two charts on this page is not that they are the last word on your product — it is that comparing them shows you what kind of question you are actually asking.